A substrate such as a silicon (Si) wafer may have a semiconductor region exposed between insulator regions, on which an epitaxial film of silicon (Si) or silicon germanium (SiGe) is formed by selective growth. In the case where the selective growth of an epitaxial film is implemented using a substrate processing apparatus, e.g., a hot-wall type CVD apparatus, a substrate such as a silicon (Si) wafer is first loaded into a reaction furnace and then the reaction furnace is heated or cooled to a target film-forming temperature. After the reaction furnace has reached the target film-forming temperature, it takes a certain amount of stabilization time sufficient to stabilize the internal temperature of the reaction furnace and the temperature of the inside of the wafer surface. Thereafter, a source gas is supplied to the reaction furnace and an epitaxial film of silicon (Si) or silicon germanium (SiGe) is formed by selective growth.
Conventionally, to reliably perform selective growth, the rear surface (opposing surface) of a substrate arranged immediately above a film-forming target substrate is made of a silicon (Si)-based material. Referring to Japanese Patent Laid-Open Publication No. Hei5-206040, for example, the rear surface of a substrate is made of a silicon (Si)-based material such as polysilicon (poly-Si). In this case, prior to performing selective growth of a silicon (Si) film or a silicon germanium (SiGe) film, the silicon (Si) on the rear surface of the substrate is exposed by wet-cleaning or dry-cleaning the substrate in the course of a substrate manufacturing step in which a natural oxide film is removed from the substrate. Thereafter, an epitaxial film is formed by selective growth.
Further, Japanese Patent No. 4394120 discloses a method without exposing silicon (Si) on the rear surface (opposing surface) of a substrate, where dummy substrates are charged into a boat at a pitch twice as great as a normal pitch and the boat is loaded into a reaction furnace to form polysilicon (poly-Si) films on the dummy substrates in advance. A product substrate is inserted between the dummy substrates having the polysilicon (poly-Si) films formed thereon. Then, the boat is loaded into the reaction furnace once again to perform selective growth of an epitaxial film.
In the aforementioned related art in which the opposing surface of a substrate is made of silicon (Si) or polysilicon (poly-Si), however, a silicon (Si)-containing film tends to obtain a stable shape when the silicon (Si)-containing film is formed on a semiconductor region of a substrate exposed between insulator regions. This may cause the migration of silicon (Si), and as a result, the shape of the silicon (Si)-containing film becomes uneven and sometimes becomes round. This problem is particularly conspicuous when performing selective growth of a thin silicon (Si) film or a thin silicon germanium (SiGe) film having a thickness of about 100 Å.